It is already known to provide headlights which are capable of producing by themselves chopped beams, such as dipped beams or beams for penetrating fog, which are bounded at the top by a well-defined cut-off line. In this connection, reference can be made to French patent specifications Nos. FR 2 536 502A and FR 2 536 503A, both in the name of Valeo Vision S.A. In these known headlights, the required width of the beam is obtained with the use of prisms and striations which are formed on the cover glass of the headlight. The design of these light-deflecting elements is generally made empirically, step by step, in such a way that the beam will have a satisfactory final photometry.
The above mentioned Company subsequently developed reflectors in which the reflective surfaces were designed to give the beam a certain width behind, i.e. upstream of, the cover lens or glass of the headlight. The cover glass in that case is then either smooth or with only a very slight light-deflecting capability, a desirable feature, firstly in terms of styling, and secondly from the optical point of view. In this latter connection, the inclination of the cover glasses in modern headlights makes it rather difficult to design the cover lens in such a way that it will provide the required horizontal spread of the beam. This state of the art is described in French patent specifications Nos. FR 2 609 146A, FR 2 609 148A, FR 2 639 888A and FR 2 664 677A.
In order to give better control of the lateral spread given to the beam, special striations have been designed, which are applied directly on the reflective surface of the reflector, in the manner described in French patent specification No. FR 2 732 446A. However, manufacture of such headlights on an industrial scale gives rise to certain difficulties. More precisely, to the extent that the horizontal spread of the beam is controlled--there being a tendency to require better and better control of this spread--the side edges of the beam become excessively sharp, so that the light disappears relatively suddenly beyond a certain angle of deflection on the right and on the left. In addition, various manufacturing errors, especially as regards the deposit of varnish on the surfaces, give a comb-like appearance to the beam in the region of these side edges.
These two errors become even more perceptible when viewed by a person using peripheral vision.
In addition, reflectors with smooth surfaces and reflectors with irregularly striated surfaces are not always considered desirable by styling designers, who nowadays look for headlight reflectors with a more original appearance, while at the same time they require to be able to produce satisfactory photometry in the beams without relying on the cover lens.